The present invention relates to a system for inspecting hot, formed metal and in particular to a method and apparatus for detecting a defect in hot formed metal, or other formed material, in real time and identifying the type, depth and extent of the defect through processing IR signature data.
Steel and other metals are fashioned into various sizes and shapes such as sheets, rods, bars or wires for end user delivery. This process usually consists of heating bulk metal billets to malleable temperature and then hot-working by forging, rolling or extrusion until the desired shape and size are achieved.
Several types of defects and faults are known to occur as a result hot working of a product. Types of flaws may include cracks, laps, overfill, fins, scabs, scratches, roll marks, fire crack transfer marks, and roughness. Some flaws will have an inherently well defined structure whereas others tend to be highly unstructured to the extent of being random. Some flaw types are global, spanning the full length of the formed stock. Others are localized. Characteristic features of some flaws may be similar. This complicates the automated defect detection processes. Inspection for such flaws requires a high degree of spatial and thermal resolution.
Currently, cold inspection is generally relied upon for quality control. Cold inspection may be performed by human observation, eddy current, magnetic flux leakage, ultrasound, and/or spectroscopy techniques, for example. Such testing is complex and labor intensive due to the occasionally subtle nature of some types of flaws, an inspected material's sheer bulk mass, and the total product area which requires inspection. Typically, only random samples of worked stock can be checked. In addition, considerable time delay can occur between the time of manufacture and corresponding quality control testing. Such time delay is highly undesirable and unduly costly if inspection shows that a production adjustment is required.
Simple, low data rate on-line autonomous systems currently exist for elementary measurements such as pyrometers for temperature measurement and laser scanners or optical shadow casting for gauging. Eddy current and pyrometer based systems are being studied and used to some extent for on-line flaw inspection. However, such techniques are only marginal and ad hoc for this task since they can only sense large and repetitive product discontinuities, require special product proximity and/or handling, and generate considerable signal ambiguity requiring highly experienced human interpretation which cannot be performed in real time.
Methods that rely on reflected light cannot detect subsurface defect structure and are subject to lighting artifacts and/or blur when used for inspecting fast moving target products. Thus, TV's, CCD's, and other such visible radiation sensitive and/or slow framing cameras are unsuitable for dynamic detection of defect type and/or depth.
Examples of conventional inspection systems include U.S. Pat. No. 4,118,732 wherein a TV camera system is used to detect reflected radiant energy and determine the existence of faults or defects based on the detected differences in captured rest images. The system described is limited to surface detection and merely detects the presence of faults or defects appearing on the product surface without providing any information as to the type, depth or extent of such defects.
U.S. Pat. No. 4,319,270 also discloses a conventional video monitoring system which detects surface faults. The patent describes a method for detecting surface imperfections on the surface of a hot material. The method involves collecting video images of the surface of a material and breaking down the images into pixel signals each having a corresponding value. Average values are calculated and variously stored for later retrieval and comparison. By comparing the present pixel values with the stored averages, variations, and thus defects, are detected. Here again, however, only surface faults are detectable. Furthermore, there is no technique disclosed for determining the type, depth or extent of any of the detected faults.
U.S. Pat. No. 4,665,317 is directed to a process for sensing surface defects on a moving strip. The process involves developing an analog signal representing the image and storing the signal for processing. The signals are converted in order to assign numerical values to each signal, and then these are filtered in order to determine if a signal represents a defect. Once again, only surface faults are detectable and there is no technique disclosed for determining the type, depth or extent of any of the detected faults. The system has no real-time capability as output data is formatted for human interpretation.
U.S. Pat. No. 4,759,072 describes a method of detecting surface flaws in a hot metal body. The method involves gathering an optical video signal and a corresponding IR video signal for a given area of the surface being inspected. Each of the signals is converted into binary data and then corresponding signals are passed through a logic gate in order to determine if a defect is present. No defect type or size determination is disclosed.
Hence, it is believed that a completely satisfactory on-line automatic inspection system currently does not exist. In addition to the aforementioned problems, conventional systems fail to account and correct for translational errors brought about by vibration or translation of the inspected product and the inspection system relative to one another.
It is an objective of the present invention to provide real time on-line automatic product inspection which offers computerized analyses, minimal special material handling, 100% inspection capability, and instantaneous inspection feedback for quality control and production process control leading to reduced waste and higher efficiency. It is a further objective to provide a system which is capable of automatically compensating and correcting for movement and translational errors occurring between the inspection system and the inspected object.
Automatically quantifying metal defects, or flaws, in real time during the hot-working process benefits production process control as well as production quality control. Simply knowing in real time that a defect is being produced is good, however knowing the type of defect and its depth and/or extent is vastly superior. Identifying the defect type offers the potential for real time feedback for production control adjustment. Knowing the depth and extent of a defect in worked metal qualifies the value of the metal being produced.
In part, the inherently hostile mill environment has prevented the introduction of on-line instrumentation for automatic flaw detection and characterization. Several problems exist in inspecting a moving product in such an environment. These include the inspection of a moving product which may travel at speeds approaching several hundred miles per hour and may have significant lateral flutter (vibration). Furthermore, such product may exist at temperatures ranging up to several thousand degrees Fahrenheit. Additionally, various levels of scale buildup are typical in such environments, which scale may have flaw masking effects or may provide false designations.
Prior art systems have failed to sufficiently address and overcome such problems. None of the present, conventional systems are believed to have a capability for detecting the type of flaw in addition to its depth and extent. Most known systems rely to a great extent on the detection, differentiation and interpretation of visible spectrum light. Consequently, such systems are entirely limited to the detection of surface flaws. It is an object of the present invention to overcome these shortcomings.